Positive electrode collector for lead acid storage battery and method for producing the same

ABSTRACT

A positive electrode current collector for lead-acid batteries contains a current collector substrate of titanium or a titanium alloy, a coating of titanium oxide formed on the surface of the current collector substrate, and a conductive ceramic layer formed on the surface of the coating, and the thickness of the coating is 0.09 μm or thinner.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a positive electrode current collectorcontaining a conductive ceramic layer formed on the surface of a currentcollector substrate of titanium or a titanium alloy and a productionmethod thereof.

2. Description of the Related Art

New materials in place of lead or lead alloy to be used for positiveelectrode current collectors for lead-acid batteries have beeninvestigated. The materials are required to have high conductivity,insolubility in electrolyte solutions, electrochemical stability inelectrolytic solutions, and high oxygen overvoltage. Conductive ceramicsmade of metal oxides, metal silicides, and the like have been known asthose which satisfy these requirements. For example, there are SnO₂,Ti_(x)Ta_((1-x))O₂, TiSi₂, TiSi₃, Ti₅Si₃, TaSi₂, NbSi₂, Nb₅Si₃, andTi₄O₇.

However, positive electrode current collectors cannot be produced onlyfrom materials of these conductive ceramics. It is because the volumespecific resistivity of such conductive ceramics is 10 Ω·cm or lower,however it is still too high as compared with those of common metals(10⁻⁶ to 10⁻⁵ Ω·cm or lower).

Therefore, it is proposed that conductive ceramic layers are formed onthe surfaces of current collector substrates of titanium or titaniumalloys to provide positive electrode current collectors of lead-acidbatteries (e.g., Electrochemistry, Vol. 47 (668), the ElectrochemicalSociety of Japan, 1979, and Electrochemistry, Vol. 48 (384), theElectrochemical Society of Japan, 1980). These positive electrodecurrent collectors are obtained by coating conductive ceramics such asSnO₂ (Sb-doped), PtO_(x), IrO₂, and RuO₂ on the surface of titanium andfurther coating β-PbO2 on the surface.

Further, also proposed are lead dioxide electrodes to be used for DSAelectrodes for electrolysis which are produced by coating surfaces ofcurrent collector substrates of titanium or titanium alloy withconductive ceramics made of PtO_(x) and further with α-PbO₂ and β-PbO₂(e.g. reference to Japanese Patent Application Laid-Open (JP-A) No.63-57791).

As described in these Documents, in the case where titanium providedwith a conductive ceramic layer on the surface is used as a positiveelectrode current collector, since the conductivity of titanium issufficiently high as compared with that of the conductive ceramic, theconductivity of the positive electrode current collector is ensured.Further, since titanium has high corrosion resistivity, it is basicallyhard to be dissolved in diluted sulfuric acid, which is an electrolytesolution. Moreover, if a conductive ceramic layer is formed, dissolutionof titanium does not become a problem. Further, since titanium has ahigh melting point, titanium can stand high temperature around 500° C.in a step of forming the conductive ceramic layer. Titanium also has acharacteristic that it is made passivated, however the passivation canbe prevented by coating of titanium with the conductive ceramic layerand therefore, the passivation does not either become a problem.Further, since titanium is more economical than conductive ceramics, thematerial cost can be saved.

Because of the above-mentioned reasons, investigations on titanium ortitanium alloys provided with conductive ceramics on the surface havebeen made.

SUMMARY OF THE INVENTION

However, in the case where a lead-acid battery is produced using apositive electrode current collector for lead-acid batteries produced byforming a conductive ceramic layer on the surface of a current collectorsubstrate of titanium or a titanium alloy, there was a problem that theinner resistance of the lead-acid battery is high. Therefore, itresulted in a problem such that the high rate discharge capacity of thelead-acid battery is not so good.

Inventors of the present invention investigated on reasons for theabove-mentioned problems and it was found that a coating of titaniumoxide between the current collector substrate of titanium or titaniumalloy and the conductive ceramic layer was a cause. That is, sincetitanium oxide with a low conductivity existed between the currentcollector substrate of titanium or titanium alloy and the conductiveceramic layer, the resistivity of the positive electrode currentcollector became high, which leads to a large internal resistivity of alead-acid battery. It is supposed that this coating of titanium oxide isproduced by oxidation of the surface layer part of the current collectorsubstrate of titanium or titanium alloy at the time of firing in thestep of forming the conductive ceramic layer on the current collectorsubstrate of titanium or a titanium alloy.

In consideration of the above-mentioned problems and causes, theinvention has been completed.

(A) The present invention is characterized in that with respect to apositive electrode current collector for lead-acid batteries providedwith a current collector substrate of titanium or titanium alloy, acoating of titanium oxide formed on the surface of the positiveelectrode current collector, and a conductive ceramic layer formed onthe surface of the coating, the thickness of the coating of titaniumalloy oxide is 0.09 μm or thinner.

According to the invention, the coating of titanium oxide formed betweenthe current collector substrate and the conductive ceramic layer issufficiently thin. Therefore, the electric resistivity is lowered.Accordingly, in the case where a lead-acid battery is produced usingabove mentioned positive electrode current collector, the lead-acidbattery becomes excellent in the high rate discharge capability.

Herein, generally, the chemical formula of titanium oxide is expressedas TiO₂. However, with respect to titanium oxide described in thisspecification, the stoichiometric ratio of titanium and oxygen is notnecessarily limited to be 1:2. Therefore, titanium oxide, which is acomponent of the coating, is expressed as TiO_(x) in the presentinvention. In this case, x is higher than 0 and 2 or lower.

The thickness of the coating of titanium oxide can be measured by Markustype high frequency glow discharge optical emission spectroscopy(hereinafter, referred to as GD-OES analysis). A practical method andconditions for the measurement will be described along with FIG. 3 inthis specification in (2.1.4) Embodiments.

In the case where the thickness of the coating of titanium oxide is 0.09μm or thinner, it is easy for a person skilled in the art to have anidea that the electric resistivity becomes smaller as the thicknessbecomes thinner.

Conductive ceramics are ceramics obtained by firing metal compounds suchas metal oxides or metal silicides at a high temperature and having avolume specific resistivity of 10 Ω.cm or less. The conductive ceramiclayer may be formed from only one layer or a layer and an other layercontaining α-PbO₂, β-PbO₂, etc. formed thereon. Even in such a case, theeffect to improve the high rate discharge capability of the inventioncan be caused.

(B) The invention is characterized in that with respect a productionmethod of a positive electrode current collector for lead-acidbatteries, the production method includes a first step of annealing acurrent collector substrate of titanium or titanium alloy in vacuum orinert atmosphere and a second step of forming a conductive ceramic layeron the surface of the current collector substrate treated in the firststep.

According to the invention, as described in (A), a positive electrodecurrent collector for lead-acid batteries with a coating thickness of0.09 μm or thinner can be produced. That is, before the conductiveceramic layer is formed on the current collector substrate of titaniumor a titanium alloy, the current collector substrate of titanium ortitanium alloy is annealed in vacuum or inert atmosphere. Therefore, dueto the recrystallization caused along with the annealing, the crystalstrains of titanium or the titanium alloy are released to increase thecrystallinity of titanium or titanium alloy.

Accordingly, even if being heated at a high temperature (e.g. 500° C.)during the process of forming the conductive ceramic layer on thecurrent collector substrate, the coating of titanium oxide is hardlyformed on titanium or the titanium alloy. As a result, the electricresistivity between the current collector substrate and the conductiveceramic layer is lowered. In the case where a lead-acid battery isproduced using the current collector substrate, high rate dischargecapability of the lead-acid battery is made excellent.

Herein, vacuum means vacuum to an extent that the coating of titaniumoxide is scarcely formed on titanium or titanium alloy during theannealing. Consequently, vacuum in this specification is preferably highdegree vacuum, however it is not necessarily required. In Examples ofthe present invention, as described below, vacuum was adjusted to be aslow as 1×10⁻⁴ Pa. The inert atmosphere means the atmosphere filled witha gas which does not cause reaction with titanium or titanium alloy andthus does not form the oxide coating or the atmosphere in which such asgas is sufficiently circulated.

The temperature for annealing may be a proper temperature at which thecrystal strains of the current collector substrate are released, and isnot limited. Further, in the annealing step, a process such that thetemperature for annealing is changed with the lapse of time may beincluded. In Embodiments of the invention, annealing at 700° C. for 12hours is mainly exemplified.

Herein, in the second step, the firing step is included. That is, thesecond step for forming the conductive ceramic layer includes a step offiring the current collector substrate such as a dip coating method or aspray thermal decomposition method. These dip coating method and thespray thermal decomposition method will be described in detail later.

(C) The invention is characterized in that in the above-mentionedproduction method, the half width of the peak with the maximum intensityin the XRD pattern of the titanium or the titanium alloy is adjusted tobe 0.38° or lower in the first step. In the above-mentioned productionmethod, when four peaks are selected in the order of highest intensitiesin the XRD pattern of the titanium or the titanium alloy, the totalvalue of intensities of the four peaks is controlled to be 85% or higherin the total value of the intensities of all peaks by theabove-mentioned first step.

According to the invention, the crystallinity of the surface of thecurrent collector substrate is sufficiently heightened and the crystalstrains are reliably released. Accordingly, even if the currentcollector substrate is heated at a high temperature for forming theconductive ceramic layer, the coating of titanium oxide is hardlyformed. Consequently, the electric resistivity between the currentcollector substrate and the conductive ceramic layer is lowered.

Herein, “all peaks” mentioned in claims of the present invention isdefined as diffraction peaks attributed to (100) plane, (002) plane,(101) plane, (102) plane, (110) plane, (103) plane, (200) plane, (112)plane, and (201) plane of titanium in the case where the currentcollector substrate is titanium. They are diffraction peaks appearing inthe case of scanning from 20° to 80° of 2θ in XRD measurement. In thecase where the current collector substrate is a titanium alloy, they arediffraction peaks which appear in the case of scanning from 20° to 80°of 2θ and have 1% or higher intensity ratio to the peak having themaximum intensity in XRD measurement.

(D) The invention is characterized in that with respect to a positiveelectrode current collector for lead-acid batteries provided with acurrent collector substrate of titanium or titanium alloy and aconductive ceramic layer, the conductive ceramic layer is formed on thesurface of the current collector substrate, and in the XRD pattern ofthe positive electrode current collector, the half width of the peakwith the maximum intensity among the peaks of titanium or titanium alloyis adjusted to be 0.38° or lower.

Further, the invention is characterized in that with respect to apositive electrode current collector for lead-acid batteries providedwith a current collector substrate of titanium or titanium alloy and aconductive ceramic layer, the conductive ceramic layer is formed on thesurface of the current collector substrate, and in the XRD pattern ofthe positive electrode current collector, when four peaks are selectedin the order of highest intensities among peaks of the titanium or thetitanium alloy, the total value of intensities of the four peaks iscontrolled to be higher than 85% in the total value of the intensitiesof all peaks.

According to the invention, with respect to the positive electrodecurrent collector, no thick coating of titanium oxide is formed betweenthe current collector substrate and the conductive ceramic layer.Therefore, the electric resistivity between the current collectorsubstrate and the conductive ceramic layer is lowered.

(E) The invention is characterized in that a lead-acid battery isprovided with the above-mentioned positive electrode current collector.Further, the invention is characterized in that a lead-acid batteryprovided with the above-mentioned positive electrode current collectoris disposed in an uninterruptible power supply.

The lead-acid battery and the uninterruptible power supply of theinvention are excellent in the high rate discharge capability.

(F) The invention is characterized in that with respect a productionmethod of a lead-acid battery provided with a positive electrode currentcollector, a production method of the above-mentioned positive electrodecurrent collector is the production method described above-mentioned.The invention is characterized in that with respect a production methodof an uninterruptible power supply containing a lead-acid batteryprovided with a positive electrode current collector, a productionmethod of the above-mentioned positive electrode current collector isthe production method described above-mentioned.

The lead-acid battery produced by the method of the invention isexcellent in high rate discharge capability. The uninterruptible powersupply produced by the method of the invention is excellent in high ratedischarge capability.

(G) The invention is characterized in that with respect to a positiveelectrode current collector for lead-acid batteries provided with acurrent collector substrate of titanium or titanium alloy and aconductive ceramic layer, crystal of titanium or titanium alloy isselectively oriented to four or less crystal planes.

In this specification, “selectively oriented to four or less crystalplanes” means that in XRD pattern, when the peaks are selected in orderof the highest intensities and the total value of the intensities of theselected peaks reaches at first 85% or higher of the total value of theintensities of all peaks, the number of the selected peaks is 4 or lower(including 4). In other words, in the case where even if 4 peaks areselected in order of the highest intensities, the total value of theintensities of the 4 peaks does not reach 85% of the total value of theintensities of all peaks, the current collector substrate having such aXRD pattern cannot be included in substrates satisfying “selectivelyoriented to four or less crystal planes”

According to the invention, since crystal strain of the currentcollector substrate is released, no thick coating of titanium oxide isformed between the current collector substrate and the conductiveceramic layer. Consequently, the electric resistivity between thecurrent collector substrate and the conductive ceramic layer can belowered.

In the case where the current collector substrate is titanium, thecrystal of titanium is preferable to be oriented selectively to threeplanes; (101) plane, (102) plane, and (103) plane. These three kindcrystal planes are examples of the crystal planes which can reliablyimprove the high rate discharge capability.

(H) The invention is based on the patent application (Japanese PatentApplication No. 2005-229826) filed to Japan Patent Office on Aug. 8,2005, and the disclosure of which is incorporated by reference in itsentirety.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an XRD pattern of a current collector substrate S₀ of titaniumbefore annealing treatment;

FIG. 2 is an XRD pattern of a current collector substrate S₃ obtained bycarrying out annealing treatment on the current collector substrate S₀;

FIG. 3 is a diagram showing the results of surface analysis of positiveelectrode current collectors U₀ and U₃;

FIG. 4 is a diagram showing the relation between the half width of thepeak with the maximum intensity and voltage decrease in the Embodiment1;

FIG. 5 is a vertical cross-sectional view showing the structure of anelectric cell of a control valve type lead-acid battery using a currentcollector substrate of titanium or a titanium alloy for a positiveelectrode plate;

FIG. 6 is a vertical cross-sectional view showing the structure of alead-acid battery comprising 4 electric cells in combination;

FIG. 7 is a diagram showing high rate discharge performance of electriccells (B₁, B₂, and B₃) of Examples of the present invention and anelectric cell (B₀) of Comparative Example;

FIG. 8 is an XRD pattern of a current collector substrate S₄ in theEmbodiment 2; and

FIG. 9 is an XRD pattern of a current collector substrate S₅ in theEmbodiment 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(1) At first, an analysis method of titanium or titanium alloy to form acurrent collector substrate will be described. The crystal state(orientation state of the surface and the half width of peaks) oftitanium and titanium alloy is analyzed by an X-ray diffractionapparatus using CuK α-ray. Specifically, while X-ray with prescribedwavelength is radiated to titanium or titanium alloy at impingent angleθ and scanned in a range of 20° to 80° of 2θ, and the intensity ofdiffracted X-ray in the range is counted. So-called X-ray diffractionpattern (XRD pattern) is obtained by plotting 2θ in the abscissa axisand X-ray intensity in the ordinate axis. Accordingly, based on thecrystal structure of titanium and wavelength of radiated X-ray, the typeof the crystal plane corresponding to a diffraction angle 2θ at which apeak of the X-ray diffraction intensity appears can be specified.

As reference, based on ICDD (International Center for Diffraction Data)card, which is collective XRD data, the correlation of the diffractionangle 2θ and the crystal plane of titanium is shown in Table 1.

TABLE 1 2θ (deg.) Crystal plane 35.06 (100) 38.40 (002) 40.15 (101)53.01 (102) 62.96 (110) 70.66 (103) 74.26 (200) 76.30 (112) 77.32 (201)

(2) Hereinafter, Embodiments 1 and 2 of the invention will be describedwith reference to FIG. 1 to FIG. 9.

(2.1) Embodiment 1

(2.1.1) Rolling

In Embodiment 1, pure titanium (JIS 1 type) is used as a currentcollector substrate. A plate type pure titanium is cold rolled to obtaina 0.1 mm-thick sheet. Cold rolling means rolling carried out atrecrystallization temperature or lower (generally normal temperature) ofthe metal. In Embodiment 1, cold rolling is described, however it isonly an example. Accordingly, the processing method may be other rollingmethods and methods other than rolling. Further, in Embodiment 1, aplate type current collector substrate is exemplified, however it isonly one example. The structure of the current collector substrate isarbitrary and may be, for example, lattice type.

The XRD measurement is carried out for the current collector substrate(hereinafter referred to as current collector substrate S₀) after thecold rolling. The XRD pattern by the measurement is shown in FIG. 1.Referring to FIG. 1 and Table 1, it is confirmed that titanium of S₀ has7 crystal planes in total; (100) plane, (002) plane, (101) plane, (102)plane, (110) plane, (103) plane, and (112) plane. Since there are alarge number of peaks in the XRD pattern of FIG. 1, titanium of S₀ isoriented in many kinds of crystal planes and the crystal orientation oftitanium is uneven. Further, since the intensities of the peaks arerelatively small and the half widths are wide, the crystallinity of thesurface of the current collector substrate S₀ is low. It is supposedbecause many crystal strains formed at the time of cold rolling processremain.

(2.1.2) Annealing

The current collector substrate S₀ is annealed at pressure (low vacuum)of 1×10⁻⁴ Pa and 700° C. The annealing duration is set to be 3 hours, 6hours, and 12 hours. The obtained current collector substrates arerespectively called as current collector substrates S₁, S₂, and S₃.Since the annealing is carried out under low vacuum, titanium is notoxidized at the time of annealing.

XRD measurement is carried out for the current collector substrates S₁,S₂, and S₃. The plane indexes of peaks with the maximum intensity andthe half widths of the peaks in the respective XRD patterns are shown inTable 2. Table 2 also shows the results of the current collectorsubstrate S₀ for which annealing treatment duration is 0 hour (asComparative Example).

TABLE 2 Annealing Plane indexes of peak with duration the maximumintensity Half width Comparative S₀ 0 hour  (002) 0.48° Example Example1 S₁ 3 hours (103) 0.41° Example 2 S₂ 6 hours (103) 0.38° Example 3 S₃12 hours  (103) 0.26°

The half width of the peak with the maximum intensity is narrowed byannealing. Further, as the annealing duration is longer, the half widthof the peak is narrowed. According to these results, the following arefound that the crystal strains existing in the current collectorsubstrate S₀ are removed by recrystallization at the time of annealingand that the removal of the stains is promoted corresponding to theduration of the annealing. In the case where it is desired to adjust thehalf width of the peak with the maximum intensity, the annealingduration and temperature may be adjusted. For example, in the case wherethe half width is narrowed, the annealing duration may be prolonged.

As a representative of current collector substrates S₁, S₂, and S₃, XRDpattern of the current collector substrate S₃ is shown in FIG. 2. ThreeXRD peaks of (101) plane, (102) plane, and (103) plane are observed inFIG. 2. Since the intensities of the peaks are significantly high andthe half widths are sufficiently narrow, it is supposed that the crystalstrains existing in the current collector substrate S₀ are almost allremoved.

(2.1.3) Formation of Conductive Ceramic Layer

After current collector substrates S₀, S₁, S₂, and S₃ are immersed in acoating solution of tin dioxide (SnO₂), the substrates are pulled out at30 cm/min. Herein, the coating solution is a solution prepared bydissolving tin tetrachloride (0.1 mole), antimony trichloride (0.03mole), and a small amount of hydrochloric acid in propanol. Thereafter,the substrates are dried at room temperature for 15 minutes. The driedcurrent collector substrates S₀, S₁, S₂, and S₃ are left at 500° C. inan electric furnace for 30 minutes. The environment at the time ofleaving them is air atmosphere. As a result, a conductive ceramic layerof tin dioxide is formed on the surfaces of the current collectorsubstrates S₀, S₁, S₂, and S₃. They are positive electrode currentcollectors. The positive electrode current collectors of the currentcollector substrates S₀, S₁, S₂, and S₃ on which the conductive ceramiclayer of tin oxide is formed are called as positive electrode currentcollectors U₀, U₁, U₂, and U₃, respectively.

The above-mentioned method is called as a dip coating method. In theEmbodiment 1, although the conductive ceramic layer formation by the dipcoating method is exemplified, however the invention is not limited tothe method. A spray pyrolysis method for spraying raw material solutionto the surface of titanium and other methods may be employed forformation of the conductive ceramic layer.

(2.1.4) Evaluation of Positive Electrode Current Collector

The positive electrode current collectors U₀ and U₃ are analyzed byGD-OES. The type of the apparatus used for the analysis is a Markus typehigh frequency glow discharge optical emission spectroscopic apparatus(JY-5000RF) manufactured by Horiba Seisakusho. The measurementconditions are sputtering rate for analysis mode; RF output of 20 W, gaspressure of 400 Pa, and anode diameter of 4 mm.

The results of the GD-OES analysis are shown in FIG. 3. In FIG. 3, theabscissa axis shows the depth from the surface of each positiveelectrode current collector. The ordinate axis shows the element weight(mass %) detected at the depth from the surface.

In both positive electrode current collectors U₀ and U₃, three layersare confirmed. The first layer in the most outer is a conductive ceramiclayer of tin dioxide. It is confirmed by the fact that the tin amount ishigh. The second layer is a layer of titanium oxide (TiO_(x)). It isconfirmed by the fact that the amount of Sn is sharply decreased and theamount of oxygen is sharply increased. The boundary of the first layerand the second layer is detected based of the flexion point of thecurves of tin and oxygen in FIG. 3. The third layer is the currentcollector substrate of titanium. It is confirmed by the fact that theoxygen amount is decreased and the detected element is almost titaniumalone. The boundary of the second layer and the third layer is detectedbased on the point at which the differential coefficient of the oxygencurve becomes almost zero.

According to FIG. 3, the thickness of the coating of titanium oxide inthe positive electrode current collector U₃ is 0.07 μm. It is thinnerthan the thickness of the positive electrode current collector U₀, thatis, 0.11 μm. It can be said that FIG. 3 apparently shows the effectobtained in the invention. In the case where the coating of titaniumoxide is to be made further thinner than 0.07 μm, the crystallinity andthe orientation of titanium or the titanium alloy for the currentcollector substrate may be made better.

Similarly, the positive electrode current collectors U₁ and U₂ areanalyzed to find that the thicknesses of the coating of titanium oxideof the positive electrode current collectors U₁ and U₂ are 0.09 μm and0.08 μm, respectively.

Next, XRD measurement of the positive electrode current collectors U₀and U₃ is carried out. As a result, the XRD pattern of the positiveelectrode current collector U₀ is not so significantly different fromthat of the current collector substrate S₀. It is because the conductiveceramic layer and the layer of titanium oxide are extremely thin andtherefore the intensities of the XRD peaks attributed to the conductiveceramic layer and the titanium oxide are very weak as compared with theintensity of the XRD peak attributed to titanium. With respect to thepositive electrode current collector U₃, results are the same.

(2.1.5) Voltage Decrease Test and its Result

Each of the positive electrode current collectors U₀, U₁, U₂, and U₃ ispinched between copper plates with a size of 30 mm×30 mm and pressurizedat a pressure of 50 kPa. While keeping such a state, 0.4 A current isapplied to these two copper plates. The voltage decrease during thecurrent application is measured. From the measurement results, theresistivity per unit surface area is calculated. The results are shownin Table 3.

TABLE 3 Resistivity per unit Half width Voltage decrease surface areaComparative U₀ 0.48° 221.4 mV 61.5 mΩ/cm² Example Example 1 U₁ 0.41°219.2 mV 60.9 mΩ/cm² Example 2 U₂ 0.38°  54.4 mV 15.1 mΩ/cm² Example 3U₃ 0.26°  52.3 mV 14.5 mΩ/cm²

The voltage decrease and the resistivity of the positive electrodecurrent collector U₀ are significant. It is supposed that the coating oftitanium oxide existing between the current collector substrate S₀ andthe conductive ceramic layer causes such an effect. On the other hand,in the case of the positive electrode current collectors U₁, U₂, and U₃,the voltage decrease and the resistivity of the positive electrodecurrent collector are slight. Further, as the annealing duration islonger, the voltage decrease and the resistivity are smaller.

The relation of the half width in Table 3 and the voltage decrease isshown in FIG. 4. In the case where the half width of the peak with themaximum intensity is 0.38° or smaller, the voltage decrease between thecurrent collector substrate and the conductive ceramic layer sharplybecomes slight. That is, it is confirmed that considerable difference ofthe effect is observed on the boundary of 0.38° half width. That is, inthe case where the thickness of the coating of titanium oxide is 0.07 μmor thinner, the effect becomes significant. Such considerable differencecannot be easily conceived by a person skilled in the art.

(2.1.6) Production of Electric Cell of Control Valve Type Lead-acidBattery

The structure of an electric cell 1 of a control valve type lead-acidbattery is shown in FIG. 5.

A battery case 4 is an insulating frame body for tightly housing apositive electrode active material 5, a separator 6, and a negativeelectrode active material 7 and sandwiched by a positive electrodecurrent collector 2 and a negative electrode current collector 3. Thebattery case 4 is provided with a gas discharge port 4 a communicatedwith outside. The aperture part of the gas discharge port 4 a isprovided with a control valve 8. In the inside of the battery case 4,the positive electrode active material 5, the separator 6, and thenegative electrode active material 7 are disposed. The positiveelectrode active material 5, the separator 6, and the negative electrodeactive material 7 are impregnated with an electrolyte solutioncontaining diluted sulfuric acid as a main component.

The inventors of the present invention produce control valve typelead-acid batteries with the above-mentioned structure. The productionmethod is practically as follows.

The above-mentioned positive electrode current collectors U₀, U₁, U₂,and U₃ on which the conductive ceramic layer of tin dioxide are formedare used for the positive electrode current collector 2. The positiveelectrode active material 5 is added to the positive electrode currentcollector 2 to produce the positive electrode plate. Herein, thepositive electrode active material 5 is a plate-like active materialcontaining mainly lead dioxide (PbO₂). The negative electrode currentcollector 3 is a copper plate (thickness of 0.1 mm) that is tin-plated(thickness of 20 to 30 μm). The negative electrode active material 7 isadded to the negative electrode current collector 3 to produce anegative electrode plate. The negative electrode material 7 is aplate-like active material containing mainly sponge-like metal lead. Theseparator 6 is obtained by forming glass fibers in a mat-like shape. Thepositive electrode plate and the negative electrode plate are layeredwhile sandwiching the separator and are housed in an electrolytic bath.The electrolytic bath is covered with a cover and the electrolytesolution is injected to produce the control valve type lead-acidbattery.

(2.1.7) Performance Evaluation of Electric Cell of Control Valve TypeLead-acid Battery

Electric cells 1 (nominal voltage 2V and rated capacity 2.3 Ah) usingthe positive electrode current collectors U₀, U₁, U₂, and U₃ as thepositive electrode current collector 2 are called respectively aselectric cells B₀, B₁, B₂, and B₃. After the electric cells B₀, B₁, B₂,and B₃ are fully charged, the high rate discharge at 6 A (equivalent to3 CA) is carried out to measure the terminal voltage alteration. Theresults are shown in FIG. 7. In this case, the discharge finishingvoltage is adjusted to be 1.6 V.

As a discharge curve for reference, the result of a control valve typelead-acid battery B_(ref) (nominal electric power of 12V, rating contentof 2.3 Ah) containing a positive electrode current collector of lead butnot of titanium is shown together. However, the results of B_(ref) isnot necessary to be compared with the results of B₀, B₁, B₂, and B₃.

As shown in FIG. 7, the terminal voltage is drastically lowered in theinitial discharge period in the case of the electric cell B₀(Comparative Example). Thereafter, the terminal voltage is decreased to1.6 V or lower within a short time. The thick coating of titanium oxidebetween the current collector substrate S₀ and the conductive ceramiclayer causes the effect.

The high rate discharge performances of electric cells B₁, B₂, and B₃are more excellent than that of the electric cell B₀. It is supposedlybecause the effect of the coating of titanium oxide between the currentcollector substrate and the conductive ceramic layer is slight.

The high rate discharge performances of electric cells B₂, and B₃ aremore excellent than that of the electric cell B₁. That the improvementextent of the high rate discharge capability becomes different issupposedly attributed to that since the annealing duration of thecurrent collector substrate S₁ is 3 hours, the half width of the peakwith the maximum intensity is higher than 0.38°, whereas the since theannealing duration of the current collector substrates S₂ and S₃ is 6hours and 12 hours, respectively, the half width of the peak with themaximum intensity becomes not higher than 0.38°. That is, also infabrication of the electric cells, it is confirmed that significanteffect difference is observed on the boundary of 0.38°. In thisinvention, in the case where the thickness of the coating of titaniumoxide is 0.07 μm or thinner, the case is supposed to be particularlypreferable.

(2.1.8) Lead-acid Battery for Uninterruptible Power Supply

The configuration of a lead-acid battery in which 4 electric cells arecombined is shown in FIG. 6. The lead-acid battery is a lead-acidbattery for uninterruptible power supply (hereinafter, referred to aslead-acid battery for UPS. UPS is abbreviation of Uninterruptible PowerSupply). The negative electrode current collector 3 of an electric cell1 is mounted on the positive electrode current collector 2 of anotherelectric cell 1 and in such a manner, four electric cells 1 are layeredin series. On the upper and lower side of the four electric cells 1,pressing members 9 and 10 made of conductive materials such as metalplates are arranged. The circumference of the electric cells 1 issurrounded with an auxiliary frame 11 made of an insulating materialsuch as resin. The pressing members 9 and 10 are respectively fixed inthe upper and lower end faces of the auxiliary frame 11 by a pluralityof screws 12 to firmly pressurize, pinch, and fix the four electriccells 1.

In each pinched and fixed electric cell 1, the separator 6 is kept inthe compression state. Due to the repelling force, the positiveelectrode active material 5 is pushed to the positive electrode currentcollector 2 by pressure of around 250 kPa gauge pressure and thenegative electrode active material 7 is pushed to the negative electrodecurrent collector 3. To obtain the pressing power by the separator 6,the material and thickness of the separator 6 may be adjusted properly.The pressing power can be changed properly in accordance with thestructure, capacity and size of the electric cell 1. Generally, thecharge discharge capability is stabilized by application of the pressureat about 100 to 400 kPa gauge pressure.

In the above-mentioned manner, the lead-acid batteries for UPS areproduced. The mass energy density and volume energy density of thelead-acid batteries for UPS are 160% and 140%, respectively in the casewhere those of the control valve type lead-acid battery using lead butnot titanium for the positive electrode plate are set to be 100%.

Next, the lead-acid batteries for UPS are disposed in uninterruptiblepower supply. The capabilities of the uninterruptible power supply areevaluated and as a result, the high rate discharge capabilities of threelead-acid batteries for UPS produced using electric cells B₁, B₂, and B₃are more excellent than that of the lead-acid battery for UPS producedusing the electric cell B₀.

(2.1.9) Others

As described above, in the Embodiment 1, the case of using pure titanium(JIS 1 type) as the current collector substrate is described. When theinventors of the invention carry out the same test as the Embodiment 1using titanium alloys (practically, three types; Ti-5Al-2.5V,Ti-3Al-2.5V, and Ti-6Al-4V) in place of the pure titanium (JIS 1 type),the same results as those in the Embodiment 1 are obtained.

That is, same in the case of using these three types of titanium alloys,the half width of the peak with the maximum intensity is narrowed byannealing. As the annealing duration is longer, the half width of thepeak is more allowed. Further, as the annealing duration is longer, thethickness of the coating of titanium oxide formed between the titaniumalloy and the conductive ceramic layer can be made thinner. The highrate discharge capability can be improved by making the thickness of thecoating of titanium oxide thin. Particularly, in the case where the halfwidth of the peak is 0.38° or lower, the significant effect isconfirmed.

(2.2) Embodiment 2

(2.2.1)

In Embodiment 2, various pure titanium (5 types) are used as a currentcollector substrate. The production processes for these 5 types of puretitanium are different from the pure titanium used in the Embodiment 1.Therefore, the XRD patterns of the 5 types of pure titanium employed inEmbodiment 2 are different from those of Embodiment 1. The 5 types ofpure titanium plates are cold rolled to obtain 0.1 mm-thick sheets.

(2.2.2) Annealing

The 5 types of plate type pure titanium are annealed at pressure (lowvacuum) of 1×10⁻⁴ Pa and 700° C. The annealing duration is set to be 12hours. Seven types of annealed current collector substrates arerespectively called as current collector substrates S₄, S₅, S₆, S₇, andS₈.

The intensities of XRD peaks corresponding to the respective planeindexes in the XRD patterns of the current collector substrates S₄, S₅,S₆, S₇, and S₈ are collectively shown in Table 5. The unit for thenumerals in Table 5 is [count/second]. The data of S₀ and S₃ used inEmbodiment 1 are also included in Table 5. In the lowest line of Table5, the total values of the intensities of the peaks appearing in therespective XRD patterns are shown. As references, the XRD patterns of S₄and S₅ are shown in FIG. 8 and FIG. 9, respectively.

TABLE 4 Comparative Example Example 3 Example 4 Example 5 Example 6Example 7 Example 8 S₀ S₃ S₄ S₅ S₆ S₇ S₈ (100) 72 47 26 191 33 133 34(002) 537 58 33 2030 67 63 91 (101) 519 864 151 1303 322 1799 323 (102)266 743 987 1008 1844 1532 2027 (110) 317 35 53 100 80 39 87 (103) 5211598 2009 1399 2874 1200 2899 (200) 21 9 10 16 13 18 25 (112) 460 51 42103 18 55 34 (201) 45 26 19 84 20 45 11 Total 2758 3431 3330 6234 52714884 5531 value

Next, with respect to each XRD pattern of the respective currentcollector substrates S₀, S₃, S₄, S₅, S₆, S₇, and S₈ in Table 4, twopeaks with the highest intensities are selected and the ratio of thetotal value of the intensities of these selected two peaks to the totalvalue of the intensities of all peaks is investigated. Similarly, theratios in the case where three peaks are selected and in the case wherefour peaks are selected are also investigated.

To make understanding easy, an example of the case of the currentcollector substrate S₃ will be described practically. If two peaks ofthe current collector substrate S₃ are selected in the order of thehighest intensities in accordance with Table 5, they are of (103) planeand (101) plane. The total value of the intensities of these two peaksis (2462 (=1598+864)). The value is about 71.8% to the total value(3431) of the intensities of all peaks. Similarly, if three peaks areselected in the order of the highest intensities, they are of (103)plane, (101) plane, and (102) plane. The total value of the intensitiesof these three peaks is (3205 (=1598+864+743)). The value is about 93.4%to the total value (3431) of the intensities of all peaks.

The above-mentioned investigation results are shown in Table 5.

TABLE 5 Comparative Example Example 3 Example 4 Example 5 Example 6Example 7 Example 8 S₀ S₃ S₄ S₅ S₆ S₇ S₈ Number 2 38.4 71.8 90.0 55.089.5 68.2 89.1 of the 3 57.2 93.4 94.5 75.9 95.6 92.8 94.9 selected 473.9 95.1 96.1 92.1 97.1 95.5 96.5 peaks Number of 5 3 2 4 2 3 2orientations

According to Table 5, with respect the current collector substrate S₀,even if 4 peaks are selected in the order of the highest intensities,the total value of the intensities of the selected 4 peaks is 73.9%,which does not satisfy 85% or higher, in the total value of theintensities of all peaks. In the case where 5 peaks are selected in theorder of the highest intensities, the total value of the intensities ofthe selected 5 peaks becomes 85% or higher. Accordingly, in thisspecification, the number of the orientations of the current collectorsubstrate S₀ is counted to be 5.

On the other hand, with respect to the current collector substrates S₃,S₄, S₅, S₆, S₇, and S₈, in either one of the cases the number of thepeaks selected is 2, 3, and 4, the total value of the intensities ofselected peaks becomes 85% or higher in the total value of theintensities of all peaks.

(2.2.3) Formation of Conductive Ceramic Layer

A conductive ceramic layer is formed on each of the current collectorsubstrates S₄, S₅, S₆, S₇, and S₈. The method is same as that describedin (2.1.3). The positive electrode current collectors obtained byforming the conductive ceramic layer of tin dioxide on the currentcollector substrates S₄, S₅, S₆, S₇, and S₈ are respectively called aspositive electrode current collectors U₄, U₅, U₆, U₇, and U₈.

(2.2.4) Evaluation of Positive Electrode Current Collector

The positive electrode current collectors U₄, U₅, U₆, U₇, and U₈areanalyzed by GD-OES analysis. The analysis method is same as thatdescribed in (2.1.4). As a result of the analysis, the thicknesses ofthe coating of titanium oxide in the positive electrode currentcollectors U₄, U₅, U₆, U₇, and U₈ are 0.04 μm, 0.06 μm, 0.05 μm, 0.06μm, and 0.03 μm, respectively.

(2.2.5) Voltage Decrease Test and its Result

The voltage decrease test is carried out for the positive electrodecurrent collectors U₄, U₅, U₆, U₇, and U₈. The test method is the sameas that described in (2.1.5). The results are show in Table 6.

TABLE 6 Number of Resistivity per unit orientations Voltage decreasesurface area Comparative U₀ 5 221.4 mV  61.5 mΩ/cm² Example Example 3 U₃3 52.3 mV 14.5 mΩ/cm² Example 4 U₄ 2 45.0 mV 12.5 mΩ/cm² Example 5 U₅ 461.6 mV 17.1 mΩ/cm² Example 6 U₆ 2 43.9 mV 12.2 mΩ/cm² Example 7 U₇ 359.0 mV 16.4 mΩ/cm² Example 8 U₈ 2 44.3 mV 12.3 mΩ/cm²(2.2.6) Production of Control Valve Type Lead-acid Battery andPerformance Evaluation

Control valve type lead-acid batteries are produced using the positiveelectrode current collector U₄, U₅, U₆, U₇, and U₈ as a positiveelectrode current collector in the same manner as described in (2.1.6).The control valve type lead-acid batteries are called as electric cellsB₀, B₃, B₄, B₅, B₆, B₇, and B₈. Using these electric cells, theperformance evaluation, same as described in (2.1.7) is carried out.

In the electric cell B₀, the terminal voltage is sharply decreased inthe initial discharge period and the terminal voltage is decreased to1.6 within a short time as it is described above. On the other hand, thehigh rate discharge performances of the electric cells B₃, B₄, B₅, B₆,B₇, and B₈ are better than that of the electric cell B₀. It issupposedly attributed to that formation of the coating of titanium oxidebetween the current collector substrate and the conductive ceramic layeris suppressed.

(2.2.7) Others

In Embodiment 2, the case of using various types of pure titanium (JIS Itype) as the current collector substrate is described. When theinventors of the invention carry out the same test as the Embodiment 2using titanium alloys (practically, three types; Ti-5Al-2.5V,Ti-3Al-2.5V, and Ti-6Al-4V) in place of the pure titanium (JIS 1 type),the same results as those in the Embodiment 1 are obtained.

The invention relates to a lead-acid battery to be employed widely inindustrial fields. The invention lowers the inner resistivity of thelead-acid battery and improves the high rate discharge performance andaccordingly is outstandingly advantageous in terms of the industrialvalue.

What is claimed is:
 1. A production method of a positive electrodecurrent collector for lead-acid batteries, comprising: annealing acurrent collector substrate made of titanium or titanium alloy in vacuumor inert atmosphere such that a half width of a peak with a maximumintensity in an XRD pattern of the titanium or titanium alloy becomes0.38° or lower, wherein titanium in the current collector substrate isnot oxidized during annealing, applying a coating solution includingSnO₂ on a surface of the current collector substrate, and firing thecurrent collector substrate to form a titanium oxide coating on thesurface of the current collector substrate and a conductive ceramiclayer of SnO₂ on the titanium oxide coating, wherein the titanium oxidecoating exists such that a thickness of the titanium oxide coating is0.08 μm or less.
 2. A production method of a positive electrode currentcollector for lead-acid batteries, comprising: annealing a currentcollector substrate made of titanium or titanium alloy in vacuum orinert atmosphere such that when four peaks are selected in the order ofhighest intensities in the XRD pattern of the titanium or the titaniumalloy, the step of the annealing makes the total value of intensities ofthe four peaks be 85% or higher in the total value of the intensities ofall peaks, wherein titanium in the current collector substrate is notoxidized during annealing, applying a coating solution including SnO₂ ona surface of the current collector substrate, and firing the currentcollector substrate to form a titanium oxide coating on the surface ofthe current collector substrate and a conductive ceramic layer of SnO₂on the titanium oxide coating, wherein the titanium oxide coating existssuch that a thickness of the titanium oxide coating is 0.08 μm or less.3. A production method of a positive electrode current collector forlead-acid batteries according to claim 1, wherein a thickness of thetitanium coating is 0.07 μm or less and more than 0.03 μm.
 4. Aproduction method of a positive electrode current collector forlead-acid batteries according to claim 2, wherein a thickness of thetitanium coating is 0.07μm or less and more than 0.03 μm.